1. Field of the Invention
The present invention relates to image compression encoding, and more particularly, to a prediction method for an inter-picture which improves image compression efficiency, and an apparatus and method for image encoding/decoding using the prediction method.
2. Description of the Related Art
In video compression standards such as moving picture expert group (MPEG) MPEG-1, MPEG-2, MPEG-4 Visual, H.261, H.263, and H.264 standards, an image is compressed through interprediction that refers to previous or following pictures for video encoding.
FIG. 1 is an illustration for explaining a conventional interprediction method. A conventional encoder calculates a motion vector for a macroblock within a frame to be interpredicted, i.e., a prediction frame 110. The encoder does a search in a search area 122 of a reference frame 120 for interprediction. To search in the search area 122 for a candidate macroblock that is best matched with a current macroblock 112 of the prediction frame 110, the encoder compares the current macroblock 112 with a plurality of candidate macroblocks in the search area 122. The encoder outputs information indicating an entropy-encoded motion vector for the best matched macroblock.
Since a motion vector correlates with its surrounding motion vectors, data used for transmission of motion vector information is compressed by selecting a motion vector predictor from neighboring macroblocks of a current macroblock and predicting a motion vector for the current macroblock using the selected motion vector predictor. The encoder encodes a difference between the predicted motion vector and the selected motion vector predictor. A decoder adds the difference to the motion vector predictor to reconstruct a motion vector and calculates a prediction macroblock for the current macroblock 112 using the reconstructed motion vector based on information of the previously reconstructed reference frame 120. Since the prediction macroblock obtained through interprediction is not completely matched with the current macroblock 112, the encoder obtains and encodes an error block or a residual block including a pixel difference between the prediction macroblock and the current macroblock 112.
However, there is a need for an improved encoding method capable of improving compression efficiency to provide high-definition videos to users using a fixed bandwidth.